In a prior art combined hot water supply and space heating system 1 shown in FIG. 1, cold water from a mains supply 2 is heated by a boiler 4 and stored in a hot water tank 6 having a heat exchange coil 8. Hot water from the hot water tank 6 is conveyed through pipes to outlets 10 and 12 which may, for example, be hot water taps and which are distributed around a building at different locations or areas 14 and 16 respectively. Each location 14 or 16 may, for example, be a room or a flat. In response to demand for hot water at the hot water outlet 10, hot water is drawn from a tank outlet 18 located towards the top of the hot water storage tank 6. The hot water drawn from the hot water storage tank 6 is replenished with cold water from the mains supply 2 via an inlet 20 located towards the bottom of the hot water tank 6.
In general, cold water outlets such as cold water taps 22 and 24 are also located with the hot water outlets 10 and 12 respectively. In response to a demand for cold water at cold water outlets 22 and 24, cold water is supplied from the mains supply 2.
When producing hot water on a commercial scale, there is generally a background level of substantially constant (mean) hot water usage. Therefore, in order to satisfy a peak demand, either a large hot water tank is required such that the water in such a tank can be heated when the boiler (which should be construed to include a heater) has a spare capacity to do so, or alternatively, the boiler must be rated for the maximum expected demand and hence a larger and more expensive boiler system is required which generally runs at below its peak capacity. In the former case the capacity of the hot water storage tank is likely to be of the order of several hundred liters. Once the hot water stored in such a large tank is depleted, it can take a long time for the boiler to heat the cold water drawn into the tank to replenish the hot water drawn from the tank. This can be particularly problematic when the different areas 14 or 16 are not located in the same private residence. If area 14 corresponds to a first flat occupied by a first user and area 16 corresponds to a second flat occupied by a second user, for example, neither of the first or second users is likely to be motivated to conserve hot water. Thus, the first user may exhaust the hot water stored in the hot water storage tank 6 to the detriment of the second user who will not be able to draw any hot water until the water in the hot water storage tank 6 has been heated via the heat exchange coil 8 when the boiler 4 is operated.
The combined hot water supply and space heating system 1 also comprises space heaters 26 and 28 located in areas 14 and 16 respectively. The space heaters 26 and 28 are connected in parallel across the primary circuit of the boiler 4 so that, for combined hot and cold water supply and space heating, each area 14 and 16 must be serviced by four pipes. This can be problematic especially when access is restricted as is often the case in older buildings when routing pipe-work into different areas can be time-consuming and costly.